In many applications where kink resistant tubing is used, it may be desirable to provide collapsible (non-kink resistant) tubing portions for some specific purpose, such as controlling or intentionally stopping the flow of liquid through the tubing. Kink resistant tubing is frequently used in medical applications where the consequences of inadvertently kinking the tubing and shutting off the flow of a fluid, such as blood or an IV solution, may be harmful or fatal. In many medical applications, however, a portion of the tubing is deliberately constricted or kinked to control or shut off the flow of fluid through the lumen of the tubing.
An example of such a medical application is tubing connecting a patient's circulatory system to a heart bypass circuit, which may include one or more of the following elements: a rotary peristaltic blood pump or centrifugal blood pump, oxygenator, heat exchanger and bubble trap. Exposed tubing of this type would preferably be kink resistant to prevent inadvertent obstruction of the tubing, while the portion of the tubing that is placed in a rotary peristaltic pump, for example, should be collapsible.
Another example is catheter tubing. It may be desirable to have one or more portions of such a catheter formed with some type of relatively rigid kink resistant structure, with other portions being flexible. Other medical examples include IV tubing, which may include portions that should be collapsible. A portion of the tubing may be collapsible so that a roller clamp can be used to control or restrict the flow of fluid, or so that a linear peristaltic pump may be used to regulate the flow of fluid through the tubing.
U.S. Pat. No. 3,426,744 describes a heart pump cannula of elastic material having a non-reinforced expandable portion and a reinforced non-expandable portion. The non-expandable portion of the cannula may have a sleeve of rayon or nylon cord embedded therein to prevent expansion.
Numerous examples of non-medical applications of kink resistant tubing exist where it it desirable to provide collapsible portions for some purpose, if for no other reason than to reduce the cost of the tubing. It may be desirable to provide relatively short kink-resistant sections in long tubes, in locations (e.g., along bent portions) where kinking would otherwise be likely.
However, manufacturing tubing having reinforced and non-reinforced sections in large quantities has been difficult and expensive. Kink resistant tubing has typically been manufactured for medical use by first forming a plastic tube by coating a mandrel with a thermoplastic or thermoset material, such as silicone or plastisol. A coiled wire spring is then placed around the tube. The wire spring and tube would then be dipped or run through a molten thermoplastic solution to coat the wire and tube. The coating operation may be performed repeatedly until the desired surface properties and size are obtained, and each coating layer would be cured in an oven before applying the next layer. In order to facilitate removal of the completed tube from the mandrel, pressurized air has been supplied to the mandrel to separate the tube from the mandrel by forming a type of "air bearing". Even when using an air-bearing type mandrel, it has been difficult to form long continuous sections of tubing (e.g., Continuous sections greater than 16-18in. (400-460mm) long).
U.S. Pat. No. 3,618,613, for example, describes an antithrombotic intravascular catheter reinforced with nonkinking means. The tubing described in that patent is reinforced by the application of a continuous wire spring coiled around the tubing in an interference fit. The wire spring and tubing is then coated with a layer of silicone.
Alternative manufacturing techniques have included injection molding thermoplastic material into a mold holding a reinforcing wire insert. One problem with that technique is the tendency of the wire insert to move during molding, and the impracticality of forming long continuous sections of tubing in an injection mold.
Outside of the medical field, kink resistant or reinforced tubing has frequently been manufactured by wrapping wire reinforced tape around a moving cylindrical mandrel to form a hose. As shown in U.S. Pat. Nos. 2,516,864 and 2,688,343, the tape has sometimes included specially configured lateral edges to improve bonding between adjacent sections of tape. An alternative manufacturing method apparently described in U.S. Pat. Nos. 4,459,168 and 4,479,835 is to successively wind layers of tape and a reinforcing wire around a mandrel to form wire reinforced hose.
U.S. Pat. No. 4,350,547 describes a method of making flexible hose by among other things co-extruding a rigid resin reinforcement wire in a body of nitrile rubber to form a rubber strip. The rubber strip is wrapped around a former or mandrel to form flexible hose, and heat is applied to vulcanize the rubber portion of the hose.
One problem with the methods discussed above for manufacturing medical and non-medical grade tubing is that they are not designed to continuously form tubing having both reinforced and non-reinforced sections. Moreover, tubing formed by wrapping tape around a mandrel is believed to be unacceptable in medical applications where leaking and sterilization are special concerns. An additional problem is the need in medical applications for substantially clear tubing that does not have bubbles or defects in the tubing wall. Such bubbles would create false alarm, since they might be confused with air or gas in an IV solution or blood. The overlapped tape sections are believed to be difficult or impractical to manufacture without bonding defects or air bubbles. Any surface roughness along the seam between adjacent sections of tape may damage blood and irritate or damage body tissue, such as the walls of an artery or vein in which a tubular catheter or cannula is inserted. It is believed that the cumulative pressure drop caused by surface roughness along the seams of a long tube may be sufficient to substantially reduce the flow rate through the tube.